How should I report a coworker for potential stalking?

Hello, i’ll Make this very quick. I am at work (Zoo) and once before this guy just watches me doing work (preparing diets for some animals) and finished two cups of water while watching me. Once I was finished, he just leaves without saying a word. I reported the first time that he did that and that it made me uncomfortable. This time, however, he is legitimately following me during my daily routine. I eventually lose him and spot him trying to find me again. I would report him for this but he is too close to our supervisor (the two of them are having an affair), and I’m afraid that she will fire me if I report it. What should I do? and if it is to report it, how should I do it, seeing as we do not have an HR?
How should I report a coworker for potential stalking?
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